The present invention relates to a crystalline modification of mixtures of a nickel-quencher and a benzophenone.
More specifically, the present invention relates to a crystalline modification of mixtures of a nickel-quencher corresponding to [2,2xe2x80x2-thiobis(4-t-octylphenolate)-n-butylamine Nickel (II)] and a 2-hydroxy-4-alkyloxybenzophenone corresponding to 2-hydroxy-4-n-octyloxybenzophenone, a process for its preparation and its use as a light stabilizer for agricultural films based on polyolefins or polyolefinic copolymers.
The present invention also relates to agricultural films based on polyolefins or polyolefinic copolymers stabilized with the above crystalline modification and greenhouses covered with these films.
Nickel-quenchers are at present sold in fine powder form and their use causes problems of environmental pollution, health and the safety of the operators in the feeding and handling phase.
A benzophenone is also generally used in the stabilization of agricultural films, together with nickel-quenchers.
Conventional methods for obtaining a physical form of nickel-quencher with a low powder content (for example, compaction of the powders under pressure) tested on both the nickel-quencher alone, and on mixtures of nickel-quenchers and benzophenones, have proved to be inapplicable or have not given satisfactory results.
The Applicant has now found a crystalline modification of mixtures of a nickel-quencher and a benzophenone capable of overcoming the drawbacks of the known art.
The present invention therefore relates to a crystalline modification of mixtures comprising:
(a) a nickel-quencher corresponding to [2,2xe2x80x2-thiobis(4-t-octyl-phenolate)-n-butylamine Nickel (II)] having formula (I): 
(b) a 2-hydroxy-4-alkyloxybenzophenone corresponding to the 2-hydroxy-4-n-octyloxybenzophenone having formula (II): 
xe2x80x83characterized in that it has two diffraction lines at angles 2xcex8=6.291 and 2xcex8=6.888 in the X-Ray diffraction spectrum from powders.
The X-Ray diffraction spectrum from powders is carried out using Cuxe2x80x94Kxcex1 radiation (xcex=1.54178).
In the crystalline modification of the present invention, the nickel-quencher (a) having formula (I) and the benzophenone (b) having formula (II), are used in a ratio ranging from 0.4 to 3, preferably in a ratio ranging from 1 to 2.
The nickel-quencher (a) having formula (I) is known under the following trade-names: Cyasorb UV 1084 of Cytec, or Chimassorb N-705 of Ciba.
The benzophenone (b) having formula (II) is known under the following trade-names: Lowilite 22 of Great Lakes, Chimassorb 81 of Ciba, or Cyasorb UV 531 of Cytec.
The crystalline modification of the present invention can be obtained, for example, with a process comprising the extrusion of a mixture of powders of the two components, operating at such a temperature that only a small part of the benzophenone (b), having a melting point of 47xc2x0 C.-50xc2x0 C., melts and dissolves only a small part of the nickel-quencher (a), having a melting point greater than 260xc2x0 C.
A solid xe2x80x9cspaghettoxe2x80x9d is thus obtained which, after appropriate cooling, can be granulated by cutting at the head of the extruder or by subsequent fragmentation.
The molten part of the benzophenone (b) and the part of the nickel-quencher (a) dissolved therein, on resolidifying, act as a binder for the remaining components, benzophenone (b) and nickel-quencher (a), which are still in powder form: in this way the solid xe2x80x9cspaghettoxe2x80x9d is obtained, which is subsequently cooled and cut as described above.